Electrical filter



Aug. 1, 1933. B, CROUSE 1,920,948

ELECTRICAL FILTER Original Filed Jan. 27, 1928 Z I 6 ,5 J6

"'Amp.

H :22 01:: J (J l +081? J vTa" 1% T ouuun noun C F I jwvenlot Patented Aug, l,l933 I l I c UNITE-D STATES-J PATENT orriceif George B. Grouse, New York, N. Y., assignor, by

mesne assignments, to Byrnes, Townsend & Potter, Washington, D. 0., a firm consisting of Charles H. Potter, James F. Pierce and Richard L. Schefiler Application January 27, 1928, Serial No. 249,917 r Renewed November 7, 1932 a 12 Claims. (01.17844) This invention relates to electrical filters and Which effect a maximum-suppression at the lower p r icularly to electrical filters of the, type emrange of frequencies present in rectified current. ploying shunt resonant paths for preventing the In Fig. 3 of the Hull patent, there is shown a flow of alternating components to a, load circuit. combination of rectifier and filter which in itself An importantapplication' of the invention is could be given, by proper designing,vthe desired 60 found in connection with power supply devices characteristic of maximum suppression at a prefor energizing the audions of a radio receiver determined frequency, but such a supply circuit from rectified current such as delivered by direct would be'unsuitable for use with either the plate current power lines or by rectifiers energized or filament circuits of audions, .It is possible to from alternating current power lines. proportion the inductance ,14 andlcondenser 16 to 65 In my copending application, sci. No. 680,096, ma the shuntpeth resonant at t f qu y filed Decemberl2, 1923, now Patent No. 1,804,859, of the most disturbing alterna in r' n granted May 12,1931, I have pointed out that an out such a filter, if associated with either the economical filter for eliminating alternating curplate or filament circuits of a radio receiver will rent ripples fromrectified current should have not function in a satisfactory manner. The rea- 70 such characteristics that the maximum suppressons for the failure will be apparent when consion occurs at substantially the frequency of the sideration is given to the properties of. the audion most disturbing alternating component,'and a circuits; The impedance of the filamentcircuit high suppression is had for all other frequencies. is so low that the internal losses in'the resonant 20 The most disturbing alternating component may circuit could be reduced to a value lower than 5 1 or may not be the component of greatest magnithat of the filament circuit only by the use of tude, dependinguponthe frequency of the alterinordinately large and expensiveimpedance elenating current .source, thetype of rectification ments. On the other hand, a filter terminating employed, and the. characteristics of they direct in -a resonant circuit of this type cannot be emcurrent load circuit. For example, the full wave ployed with a plate currentsupply since'it .would 80 rectification of 25 cycle current results in pulsatintroduce into the plate circuits impedance which ing current having a 50 cyclealternating curwould affect the response curve of the" audio 9 rent component, and having components of lesser amplifiers. I i i magnitudes whichflare harmonics of that ire- An object of this invention is to provide a I quency. The and 100 cyclecomponents will be filter which employs the resonance phenomena 5 suppressed to a considerable extent by the audion for suppressing alternating currents, andwhi'ch' circuits and the reproducer while the 150 cycle will not disturb the operation of, aload circuit to component is amplified by the audions. I have which itsu'ppliesdirect current. Acfurther obfound that themost economical filter construction jBQt is to provide a filter having a shunt path 7 is obtained by designing the circuits to suppress which is resonant at the frequency to be supthe 150 cycle components, the effects of compressed, and impedance between the resonant ponents of other frequencies being substantially path" and loadcircuit energized' thr'ough the filter f eliminated when the 150 cycle componentslare for substantially isolating theresonant path from suppressed. the load'circuit, I

The types of filter circuits most commonly These-and other objects of the inventionfwill ,55 .works which do not employ resonant circuits but for supplying rectified'current to the filter may used in devices for supplying radioreceivers from be apparent from the following specification sources of rectified current are illustrated in Figs. when taken with the accompanying drawing in 1 and2of the'patent to Hull, 1,251,377, Decemwhich,

ber 25, 1917. These filters are open to the ob- 1 Figs. 1 and'2 are circuit diagrams illustrating iection that the maximum suppression is'not obembodiments of'the invention, and 1 'tained at the frequency of the components pres- Figs. 3 and 4 are electrical diagrams, for matlif ent in the rectified current but at an infinite fre ematical analysis, of V the elementary circuits I quency. To obtain therequired suppression of shown inFigs. land 2, respectively; Y

the components of relatively low frequencies, ex- "In thecircuit shown-in Fig. 1 of the drawing,

5 pensive and bulky constructions :must be "emthe numeral 1' identifies'the primary of'atrans aployed. Inxmy copending applications, Ser.i No. former having an 'iron core2 andasecondary 3, r 680,096, (Patent No. 1,804,859), and Ser; No. the secondary being tapped at. its midpoint, to 130,252, filed December '12, 1923, and August 19, feed-energy to a full wave rectifier 4. So faras 1926, respectively, I have described filter netthe present inventionis concerned, the apparatus Y ductance 7 and the capacity 8, a second iron core inductance 9 and the terminating condenser l0.-

The customary voltage reducing resistance 11 and by-pass condenser 12 are arranged across the output of the filter network-for supplying intermediate voltages, for example to the detector plate circuit of a radio receiver 13. :The

connections to the radio receiver are made in" the usual manner.

The inductance 7 and condenser 8 of the shunt path are so proportioned as to. be resonant. at the frequency of the most disturbing alternating current component present in the rectifier output,'

and therefore this circuit presents a substantially zero impedance shunt path for that frequency. The presence of the series inductance 9; which has arelativ'ely'high impedance, makes it possible to terminate the mesh in any manner which may. be necessary to the proper cooperation of the filter with the load circuit.

.In the circuit of Fig. 1, the inductances may be so positioned that there is substantialiyno coupling between inductance-7 and the seriesinductances, or the arrangement may be such that two or more of the inductances are coupled.

The filter shown in Fig. 2 has the same general constructionjas that of Fig.1, the only essential difference being that the separate in- V 35 ductance 7 is replaced by a winding '7 on the core ofseries inductance 6. The winding '7 is preferably tapped, into the positive lead .of the filter'at an intermediate point in the inductance 6. The other elements of the filter ne work are or may be identical with the corresponding elements of the Fig. 1 circuit, are identified by like reference numerals. The inductance 6 is a continuous winding and the direction of winding of inductance '7' is such that, with the source and; load connectedas shown in the Fig.,2,-the mutual inductances are both positive, i. e-.,,the flux produced by current flow in each winding reinforces the flux-due to current flow in the other-windings,

Q .A' mathematical analysisof the circuits will show that they may be designed -to have the same alternatingjcurrent characteristics. For the purpose ofthis-analysis, the resistance of the circuits and. theirnpedance of the load and supply circuits may be neglected. I i v The .elementaiycircuits of Fig. 1 are shown in Fig. 3', the values of the impedances of the filter mesh being represented by the capacities C1, C0, C2

andthe inductancesL1, 112.. An; alternating current; electromotive force E of the frequency of the; most disturbing component of the rectified current is shown in series with capacity C1 which represents the capacity value ofwthecondenser 5. The twoflelementary circuits are linked-by the common elements Lo, Co which representgthe values ofthe impedances of the shunt path.-

By evulating the instantaneous voltages in the two. circuits and solving theresulting simultaneous diiferential equations for'the 'Steadystate condition, it willubefoundthatthe vector amplitude of the current in circuit II, interms of voltage E in circuit I; is given bythe equation: a I

where m is the mutualimpedance between the circuits andZ1, Z2 have the following values:

1 m o The mutual impedance m between circuits I-and .II is gi ven by the equation: 7

T ZFCO It is obvious-that m may be made equal to zeroat a given frequency' by a proper choice of the relative 'valuesor L0 #and Co, and that when .m is equal to} zero, the alternating current in circuit II is reduced to zero.

Theelernentary circuits I and II of the Fig. 2 network are represented in Fig. 4. The inductances 6' and '7' on a common core result in inductance L1 and L20 in circuits I and IIQrespec tively, and mutual inductance lVI and M Ibet ween inductance 7 and the sections of inductance'fi which 'lie {in circuits I and II,-respectively. .It will be seen-at once that an analysis of this. circuit will lead to the same equation for current I2, the only'di'fferenc'e being that the mutual inductance between L1, L0 and Lie affects the'quantity ml The valueso'f Z1 and Z2 are given by the following equations:

.. 1 .1 I I+ O+ MLiL CI' TOJ 1 2 L20+ 2-l wL (,uM The mutual impedance m between circuits '1 and Ilis M= w L1 +'L0+2\ L1L 0 (Lars n/Lon) It is obvious that the quantity in may be-made equal'to zero for a .givenirequency, and therefore the network of FigaZmay; be made the electrical equivalent of the:network of Fig. l.

The'circuit of Fig. 2 permits a more compact and more economical. construction than that of Fig; l,fsince the, windings-6 and 7 maybe proportioned to eifecta substantial reduction in the number of tlll'ilS'WhiCh carry direct currentflfor a given effective value of-.s'eries-inductance, and thisreduction in .direct current ampere turnsresults in. a still further increase. in the inductance of this "element for a giveniphysical size' of the parts. m This application. is :a continuation in part of mycopending application Serial No. 1,300,252, filed August .19,1926;:' I

Iclaim: "1.=In.-an electrical filter for use between a sourceof current having alternating components an'd an audion circuit, thecombination' with eleimpedance serially connected in the line between 145 i said shunt path and theaudion circuit. terminals of'saidfilter. 2. The invention as set forth in claim 1, wherein said resonant shuntipa'th is coupled'mag-neti- 'cally' to said series impedances in .suchsense that 5 as viewed in the direction of current propagation, the couplings are positive.

3. An electrical filter for eliminating alternating current components from direct current passed to an audion circuit, said filter comprising input terminals for connection to a source of rectified current, output terminals for connection to an audion circuit, and a transmission line between said sets of terminals; said transmission line including in one side thereof a plurality of series inductive elements having positive mutual inductance, and a shunt arm connected across said line intermediate two of said series inductive elements, and comprising an inductive element and a capacity'in series, said shunt inductive element being magnetically coupled to the two adjacent series inductive elements in such sense that the mutual inductances, as viewed in the line of current propagation, are positive.

4. The invention as set forth in claim 3, wherein said series inductive elements between which said shunt path terminates comprise a single continuous winding having an intermediate tap for receiving the connection from said shunt path.

5. The invention as setforth in claim 3, wherein said series inductive elements between which said shunt path terminatescomprise a single continuous winding having an intermediate tap for receiving the connection from said shunt path, and said shunt inductive element comprises a winding wound in the same direction as viewed from said input circuit terminals, as said continuous winding.

6. In a filter for use between a source of rectified current and a direct current audion circuit, an iron core having an inductance thereon, a

second inductance on said core and connected to an intermediate point in said first inductance, said first inductance comprising a series element in one direct current lead to said audion circuit, a condenser connected in series with said second inductance to complete a resonant shunt circuit across the direct current line to said audion circuit, and a filter mesh between said shunt circuit and the audion circuit, said mesh comprising a series impedance and a shunt capacity of such relative values that the signal current flow in said audion circuit is rendered independent of the impedance of said shunt circuit.

7. In apparatus for energizing an audion .circuit from a source of rectified current, a series impedance, a circuit shunted across the supply line at the audion circuit side of said impedance, said j circuit being resonant at substantially the frequency of the most disturbing alternating component present in the rectified current, and a high series inductance between said shunt circuit and the audion circuit.

8. In apparatus for energizing an audion circuit from a source of rectified current, an impedance network for suppressing alternating" components of the rectified current, said network plate comprising a shunt circuit resonant at a fre quency to be suppressed, and a filter section between said shunt circuit and said plate. circuit to render the fiow of signal current inthe plate circuitgindependent of the impedance of said shunt circuit.

9. In apparatus for energizing an audion plate circuit from a source of rectified current, an impedance network for suppressing alternating components of the rectified current, said network comprising a shunt circuit resonant at a frequency to be suppressed, and a series inductance between said resonant shunt circuit and the said audion plate circuit, said series inductance having a high impedance to prevent said resonant circuit from affecting the flow of signal currents in said 7 signal current fiow in said circuit is independent of-the impedance of said shunt arm.

11. The invention as set forth in claim 10,,

wherein the series impedances of said filter sec tion'are substantially free from negative magnetic coupling. 7 3 i 12. The invention as set forth in claim 10,

wherein the series'impedances of said filter section' comprise series inductances having positive mutual inductance, and the inductance of, said shunt arm is magnetically coupled to said series inductances to provide positive mutual inductances as viewed in the direction of current propagation. V v GEORGE B. CROUSE. 

